1. Field of the Invention
This invention concerns a process for preparing ethylidene-bis-acetamide from acetaldehyde and acetamide and optionally thereafter converging the ethylidene-bis-acetamide to vinylacetamide.
2. The Prior Art
U.S. Pat. No. 4,018,826, issued on Apr. 19, 1977, to my coworkers, Richard Gless, Daniel J. Dawson, and Robert E. Wingard, discloses a process for preparing the useful active polymer poly(vinylamine) wherein acetaldehyde and acetamide are formed into ethylidene-bis-acetamide which is then cracked to yield vinylacetamide which is polymerized and hydrolyzed to poly(vinylamine). In the reference patent acetaldehyde and acetamide are reacted in liquid phase in the presence of a liquid strong mineral acid. While this method is effective, it has the failings of not always giving reproducible color and quality product and of requiring laborious and expensive separation of the ethylidene-bis-acetamide from the liquid acid phase. Other references to the condensation reaction of acetaldehyde and acetamide in the prior art include V. v.Richter, Ber. 5, 477 (1877); W. Noyes et al., J. Am. Chem. Soc., 55, 3493 (1933) and Ben Ishai et al., Tetrahedron Letters, 50, 4523 (1965). Also, a general review article on the condensation of aldehydes and amides may be found at Organic Reactions, 14, 52 (1965). The present invention is an improved method for carrying out this reaction of acetamide and acetaldehyde.